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Full text of "NASA Technical Reports Server (NTRS) 19930019581: Clementine 2: a Double Asteroid Flyby and Impactor Mission"

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LP1 Technical Report 93-02 3 

One of the most fundamental pieces of information about any 
planetary body is the elemental and mineralogical composition of its 
surface materials. We are developing an instrument to obtain such 
data at ranges of up to several hundreds of meters using the 
technique of Laser-Induced Breakdown Spectroscopy, or LIBS. We 
envision our instrument being used from a spacecraft in close 
rendezvous with small bodies such as comets and asteroids, or 
deployed on surface-rover vehicles on large bodies such as Mars and 
the Moon. The elemental analysis is based on atomic emission 
spectroscopy of a laser-induced plasma or spark. A pulsed, diode- 
pumped Nd:YAG laser of several hundred millijoules optical 
energy is used to vaporize and electronically excite the constituent 
elements of a rock surface remotely located from the laser. Light 
emitted from the excited plasma is collected and introduced to the 
entrance slit of a small grating spectrometer. The spectrally dis- 
persed spark light is detected with either a linear photo diode array 
or area CCD array. When the latter detector is used, the optical and 
spectrometer components of the LIBS instrument can also be used 
in a passive imaging mode to collect and integrate reflected sunlight 
from the same rock surface. Absorption spectral analysis of this 
reflected light gives mineralogical information that, when com- 
bined with the elemental analysis from the LIBS mode, provides a 
complete remote geochemical characterization of the rock surface. 

We have performed laboratory calibrations in air and in vacuum 
on standard rock powders to quantify the LIBS analysis. We have 
performed preliminary field tests using commercially available 
components to demonstrate remote LIBS analysis of terrestrial rock 
surfaces at ranges of over 25 m, and we have demonstrated compat- 
ibility with a six-wheeled Russian robotic rover vehicle. Based on 
these results, we believe that all major and most minor elements 
expected on planetary surfaces can be measured with absolute 
accuracy of 10-15% and much higher relative accuracy. We have 
performed preliminary systems analysis of a LIBS instrument to 
evaluate probable mass and power requirements; results of this 
analysis are summarized in Table 1. 

IMP ACTOR MISSION. R. J. Boain, Jet Propulsion Laboratory, 
Pasadena CA 9 1 1 09, US A. 

Recently JPL was asked by SDIO to analyze and develop a 
preliminary design for a deep-space mission to fly by two near-Earth 
asteroids, Eros and Toutatis. As a part of this mission, JPL was also 
asked to assess the feasibility of deploying a probe on approach 
to impact Toutatis. This mission is a candidate for SDIO’s 
Clementine II. 

SDIO’s motivations were to provide further demonstrations of 
precision, autonomous navigation for controlling the flight paths of 
both a spacecraft and a probe. NASA’s interest in this mission is 
driven by the opportunity to obtain the first close-up images and 
other scientific measurements from a spacecraft of two important 
near-Earth objects. For Toutatis this is especially important since it 
was observed and imaged extensively just last December using 
Earth-based radar; Clementine II will provide the opportunity to 
corroborate the radar data and validate the ultimate potential of the 

radar technique. 

Scientifically, the probe impact at Toutatis will allow the ac- 
quisition of data pertaining to the dynamic strength of surface 
material and data on the properties of the regolith and on stratifica- 
tion below the surface, and will potentially allow the measurement 
of thermal diffusivity between the interior and the surface. These 
determinations will be accomplished by means of high-resolution 
imagery of the impact crater and its surroundings in visible, 
ultraviolet, and infrared wavebands from the spacecraft flying by 
some 30 min after the probe strike. In addition, if the spacecraft can 
be equipped with a lightweight mass spectrometer and dust ana- 
lyzer, the potential also exists to measure the particle sizes and 
distribution and the composition of the ejecta cloud. 

This mission is planned to be launched in July 1995, with the 
Eros encounter on March 13, 1996, and the Toutatis flyby on 
October 4, 1 996, some 440 days after launch. The Eros encounter is 
characterized by a flyby speed of 8.4 km/s and a Sun-target- 
spacecraft phase angle of 120°. Thus, the principal visible light 
images of Eros will be obtained after closest approach. The Eros 
miss distance is nominally set at 30 km. For Toutatis, the encounter 
is characterized by an approach speed of 1 7.8 km/s and a phase angle 
of 20°. With this approach geometry, Toutatis presents a sunlit face 
to the spacecraft and probe. The probe will hit the asteroid at 
approximately 1 8 km/s. To facilitate imagery of the impact crater 
and to assure continuous line-of-sight tracking through encounter, 
the closest approach distance at Toutatis is selected to be 50.0 km. 

N 9 3 - m 

B. E. Burke, R. W. Mountain, J. A. Gregory, J. C. M. Huang, M. J. 
Cooper, E. D. Savoye, and B. B. Kosicki, Lincoln Laboratory, 
Massachusetts Institute of Technology, P.O. Box 73, Lexington MA 
02173-9108, USA. 

We describe recent technology developments aimed at large 
CCD imagers for spacebased applications in the visible and UV. 
Some of the principal areas of effort include work on reducing 
device degradation in the natural space-radiation environment, 
improvements in quantum efficiency in the visible and UV, and 
larger-device formats. One of the most serious hazards for space- 
based CCDs operating at low signal levels is the displacement 
damage resulting from bombardment by energetic protons. Such 
damage degrades charge-transfer efficiency and increases dark 
current. We have achieved improved hardness to proton-induced 
displacement damage by selective ion implants into the CCD 
channel and by reduced temperature of operation. To attain high 
quantum efficiency across the visible and UV we have developed a 
technology for back-illuminated CCDs. With suitable antireflection 
(AR) coatings such devices have quantum efficiencies near 90% in 
the 500-700-nm band. In the UV band from 200 to 400 nm, where 
it is difficult to find coatings that are sufficiently transparent and can 
provide good matching to the high refractive index of silicon, we 
have been able to substantially increase the quantum efficiency 
using a thin film of Hf0 2 as an AR coating. These technology efforts 
have been applied to a 420 x 420-pixel frame-transfer imager, and